1. Field of the Invention
The present invention generally relates to a range measuring device, and more particularly relates to a laser riflescope with enhanced display brightness.
2. Description of Prior Art
A laser riflescope generally includes a laser emitter, a laser receiver, and a telescope system. The laser emitter is adapted for transmitting an invisible laser light beam to a target to be measured. The target reflects and returns the laser light beam to the laser receiver, which is commonly an avalanche photo diode (APD) to convert the optical signal into an electric signal. The distance between the laser riflescope and the target is calculated according to the time interval between the emission and reception of the laser light beam. The telescope system, which is used for the user to identify and aim at the target, generally includes an objective lens group, an eyepiece group, and a prism group arranged between the objective lens group and the eyepiece group. However, in practical use, if the laser emitter, the laser receiver, and the telescope system, each of which is composed of several lenses, have their respective optical axes, the volume of the laser riflescope will be significantly increased. Furthermore, this will also lead to a poor range measurement precision since the path of the invisible laser light beam for range measurement and the path of visible light beam for observation of the user are spaced from each other.
To address the above problems, U.S. Pat. No. 6,441,887, which is assigned to the same assignee as the present invention, provides a solution as illustrated in FIG. 1. The laser riflescope 90 as disclosed by the '887 patent includes an observation/emitting optical system 91 and a receiving optical system 92. The observation/emitting optical system 91 includes an objective lens group 93, a prism group 94, a laser emitter 95, a display 96, and an eyepiece group 97. The receiving optical system 92 includes a laser receiver 98 and a prism 99. By the reflection and refraction of the prism group 94, the traveling paths of the invisible laser light beam for measurement and the visible light beam for observation are combined between the objective lens group 93 and the prism group 94. As a result, the volume of the laser riflescope 90 can be greatly reduced. Further, the measurement precision of the laser riflescope 90 is also ensured since the observation point and the measured point is the same.
The display 96 of the laser riflescope 90 is a transmissive LCD (Liquid Crystal Display) positioned within the field of view of the laser riflescope 90 for displaying the distance information of the target. After the visible light beam from the target enters into the observation/emitting optical system 91 and is transmitted through a number of lenses, the visible light beam then must penetrate through the transmissive LCD 96 for the distance information to be visible by the user. However, in this penetrating course, light loss occurs, which may reduce light output by as much as 50% and thus the display effect of the distance information. Especially, when measurement is conducted under dim lighting conditions, only a small amount of light enters into the observation/emitting optical system 91, and therefore, the distance information displayed by the LCD 96 becomes unreadable or even cannot be displayed.
Another distance information displaying method is also applied in the conventional laser riflescopes. As shown in FIG. 2, a conventional observation/emitting optical system 80 for a laser riflescope includes an objective lens group 81, a prism group 82, a laser emitter 83, a display 84, and an eyepiece group 85. The display 84 is generally an LED (Light Emitting Diode) for emitting a light beam of a narrow wavelength. This light beam is first reflected by a reflector 86, transmitted through a lens group 87, enters into the prism group 82 and is finally imaged in the field of view 88 of the laser riflescope. It is clear that, the problem of light loss still exists since the light beam is transmitted through a relatively long optical path, which leads to insufficient brightness of the displayed distance information.
Hence, a laser riflescope with enhanced brightness is desired to overcome the above-mentioned problems in the prior art.